The invention relates to an apparatus which achieves an automatic focussing of an optical system used in a microscope.
It is known to achieve an automatic focussing of an optical system by photoelectrically detecting a variation in the sharpness of an image of an object. The conventional arrangement utilizes a photoelectric transducer element which translates the distribution of illuminance of the image into a corresponding electrical signal, which is then processed in a suitable manner to achieve the focussing operation. The signal has been processed in analog form, and this resulted in a complex arrangement and a reduced processing rate as well as a level of accuracy which is less than desirable. While a digital processing system is known, it represents a mere digital version of the analog processing arrangement which failed to overcome the disadvantages mentioned above. In particular, in the application of an automatic focussing apparatus to a microscope, attention must be directed to the fact that a specimen on the microscope is not always a closely related assembly, which prevented a satisfactory focussing of high accuracy or even the focussing operation itself from being achieved.